The nature of the bleaching stages of rhodopsin will be investigated through studies of the pigment itself, studies of compounds which model the behavior of the pigment's chromophore, and studies of the electronic structure of various polyenes. The spectral and kinetic characteristics of various bleaching stages will be studied under near physiological conditions. Particular attention will be paid to the rhodopsin to prelumirhodopsin and metarhodopsin I to metarhodopsin II transitions since these are the transitions where the primary photophysical events and important physiological events, respectively, occur. Pigment studies will primarily involve bovine rhodopsin and rhodopsin from frogs (Rana pipiens). Model compound and polyene studies are also proposed which should help elucidate the nature of the primary photophysical events in the bleaching process.